T cell mediated immunity is likely to influence the progression of HIV-1 disease from asymptomatic infection to severe immunodeficiency. The HIV -1 virus is the only known human pathogen to elicit a cytotoxic T cell (CTL) response vigorous to enough to be detectable in fresh peripheral blood lymphocytes without in vitro amplification. Preliminary studies in 9 seropositive individuals have shown that CTL response to gp 160 and reverse transcriptase (RT) is dominated by the recognition of 1 or 2 isolate- invariant epitopes in HIV-1 envelopes (env) and reverse transcriptase (RT) proteins using a two step process. Epitopes will first be identified at the approximately 100 amino acid level by screening with targets infected with a set of vaccinia vectors encoding nested truncations or env and RT. Epitopes contained in gp 160 and in some regions of RT will be further refined using overlapping set if peptides. We will identify MHC class I molecules that can act as restricting elements for env and RT epitopes. We will also determine if some of these epitopes can be recognize by significant fraction of the outbred population. Such epitopes, if they exist, could be incorporated into vaccine designed to elicit cell mediated immunity. We have been able to select epitope-specific T cell lines by stimulation with peptide presented by autologous antigen presenting cells. These enriched cell lines lyse HIV-expressing targets as powerfully as HIV- specific clones but have the advantage of being easy to generate and grow to virtually unlimited cell numbers. We will use these cell lines to examine the physiological significance of the CTL response to HIV-1 in a series of in vitro studies. We will determine at what stage in infection CTL directed against env or RT can lyse infected cells, whether viral integration or replication is required or whether infection is sufficient. WE will also investigate whether CTL that recognize some epitopes are better able than others to inhibit viral replication or maintain viable CD4+ cells. We will also determine whether cytolytic mediators contained in exocytosed granules of CTL can inactivate HIV-1 for infectivity. These HIV-specific T cell lines will be adoptively transferred to SCID mice reconstituted with autologous human PBL to study if they can protect reconstituted mice from viral challenge. This model will enable us to study in vivo the relative potency of CTL that recognize different viral protein epitopes.